Current vapor abrasive blasting technology utilizes some sort of open loop control for metering an abrasive media/water mixture into the blast air stream. A common method utilizes an adjustable orifice valve to control the flow rate of water into a pressure vessel. In existing vapor abrasive blasting systems, the abrasive media flow rate is usually set during the initial setup of the machine at a job site. Once the pressure vessel is loaded with media and water, the operator will engage the system to begin blasting. While air and media are flowing from the nozzle, the blast air pressure is adjusted to the desired set point. After that, the orifice valve is adjusted until the operator believes the media flow rate is at the desired level.
The current technology still has a few drawbacks. First, the system has to be engaged and blasting in order to set and fine tune the abrasive flow rate. Second, any fluctuations in system pressures or adjustments to the blast air pressure require a subsequent adjustment and fine tuning of the blast media flow rate.